This disclosure relates to multiple optical wavelength physiological sensors and monitors, especially to pulse oximeters.
Pulse oximetry is a well-established technique for measuring oxygen saturation (SpO2) in arterial blood. SpO2 is an important parameter that relates to the adequacy of oxygen supply to peripheral tissues and organs. Pulse oximeters provide instantaneous in-vivo measurements of arterial oxygenation, and thereby an early warning of arterial hypoxemia, for example. Pulse oximeters also display a photoplethysmographic (PPG) pulse waveform, which can be related to tissue blood volume and blood flow, i.e. the blood circulation, at the site of the measurement, typically in finger or ear. Standard pulse oximeters use two wavelengths to measure the ratio of oxyhemoglobin to total functional hemoglobin, indicated as an SpO2 value. However, pulse oximeters using more than two wavelengths have also been developed to be able to non-invasively measure the levels of the other blood substances that provide important clinical information. For example, levels of other significant hemoglobin species, such as carboxyhemoglobin and methemoglobin, and total hemoglobin may be estimated if the number of wavelengths used in the pulse oximeter is increased.
Since the measurement is normally made from an anatomical extremity, such as a finger tip, pulse oximeters typically comprise a separate sensor attachable to a subject and the actual pulse oximeter device to which the sensor is connected through a cable. The sensor normally comprises two or more emitter elements, each emitting radiation at a specific wavelength, and a broad spectral band photodetector common to all emitter elements. Due to the various combinations of wavelengths that may be used to measure certain substances in blood and the variety of sensor types needed for different subjects and different measurement sites, the choice of sensors and interface cables that may be used in connection with one pulse oximeter device may be rather extensive. The different sensors along with the different cables and/or connectors to be used in connection with the said sensors make the operation of a pulse oximeter device rather demanding thus detracting from the user-friendliness of the device.
This drawback is further aggravated by the fact that the current oximeters do not inform the user about possible incompatibility and accuracy issues the user may encounter while using an incompatible sensor or a sensor that has degraded in performance.
While a certain measurement mode, i.e. the combination of wavelengths used, normally requires a particular sensor compatible with the mode, the internal operation of a measurement mode is normally fixed in terms of the utilization of the wavelengths, which may reduce the signal-to-noise ratio and the accuracy of the some measurements.